Mailblocks service simplifies challenge-response

A new e-mail service aims to put an end to spam by collecting the addresses of legitimate e-mail senders on to a master list that will take the "challenge" out of "challenge-response" for many e-mail users.

Four month-old Mailblocks Monday unveiled Challenge/Response 2.0, the latest incarnation of its patented Challenge/Response technology.

Challenge/Response is similar to technology used by other ISPs, including Earthlink.

Using the technology, Mailblocks quarantines inbound e-mail messages to its accounts, sending an e-mail "challenge" message back to the sender with a request to type a seven-digit number into a box.

The challenge requires the human sender to view a unique number displayed on a Web page and transcribe it, something computer-generated spam mailers can't do.

Once a valid response is received from the sender, the initial e-mail is retrieved from quarantine and delivered. The sender's e-mail address is then added to the user's valid sender list, enabling subsequent messages to be received without challenge.

The latest version of Challenge/Response reduces the likelihood that senders will get challenged by Mailblocks by aggregating the valid responses from all Mailblocks users, according to Phil Goldman, Mailblocks' CEO.

"We figured out this - if you send mail to me at Mailblocks, get challenged and respond, we know you're a human being," he said.

Users who complete a successful challenge-response exchange for a single Mailblocks user will not be challenged again, provided they don't begin spamming users, Goldman said.

The principle is akin to one credit card companies use with their members, he said.

"So as long as you're a member in good standing with Visa, you don't have to call them each time you need to charge something. The catch is, if you start to do something funky with your Visa card, they might block that card and force you to call them. It's the same thing here. If you start to spam, we'll start to challenge you again," he said.

Spam-like activity will not be judged simply by the volume of e-mail messages sent out, or the number of recipients for a message, Goldman said.

Instead, the Los Altos, Calif., company looks at the number of new Mailblocks recipients addressed by the sender, Goldman said.

Because Mailblocks is an e-mail service with a rapidly growing user base, the "do not challenge" list will quickly grow with Mailblocks e-mail traffic volume, something desktop antispam software can't offer, Goldman said.

"You never get challenged, but still eliminate all the spam. It's the best of both worlds," he said.

The IDG News Service is a Network World affiliate.